Hcp/fcc nucleation in bcc iron under different anisotropic compressions at high strain rate: Molecular dynamics study

Abstract

Previous researches have revealed the importance of shear and the orientation dependence in the structural transition of iron. In this work, we introduce a series of shear deformations by adjusting the strain ratio between the longitudinal ([001]) and transversal ([010] and [100]) directions, and then investigate this structural transition under different anisotropic compressions with molecular dynamics simulations. It is found that the shear deformation can lower the transition pressure notably, and even change the nucleation structure and morphology. Under 1D-dominated compression (along (001) direction), there only appears hcp nucleation with a few fcc stacking faults. For other cases, more equivalent planes will be activated and fcc structure begins to nucleate. Under 2D-dominated compression (along (010) and (001) directions), the fcc mass fraction is already over the hcp phase. At last, we compare the variations of shear stress and potential energy for different phases, and present the sliding mechanism under typical anisotropic compressions.

Atomistic Study of the Role of Defects on α → ϵ Phase Transformations in Iron under Hydrostatic Compression

“…Defects as edge dislocation and twin boundaries ease the nucleation of the hcp phase. The nucleation behavior is different to the results for pure iron single-crystals where the hcp clusters are formed randomly inside the bulk and differ in size and orientation [18,69]. The hcp phase forms at the cohesive twin boundaries as dense clusters.…”

Application of self-supervised approaches to the classification of X-ray diffraction spectra during phase transitions

“…For both, different crystal structures (allotropes) are thermodynamically stable within different pressure ranges. In particular, for iron a transition from body-centered cubic (BCC) to Hexagonal Close-Packed (HCP) is expected above approximately 13 GPa 53 , 54 . In the momentum transfer range accessible to our experiment, there are 3 Bragg reflections for the BCC, and 6 for the HCP structure.…”

AtomREM: Non-empirical seeker of the minimum energy escape paths on many-dimensional potential landscapes without coarse graining

“…The most interesting case is a simulation of solid-solid phase transition (PT) because this type of PT has a high energy barrier or/and it occurs under some special conditions [28]. We applied AtomREM to the PT in the argon crystal.…”

“…A notable thing is that we realized the elementary processes of the solidsolid PT with large energy barriers without melting of the system. In the previous paper investigating the solid-solid PT in iron [28] the PT was induced by molecular dynamics with anisotropic compression so that the barrier height is lowered. AtomREM does not require such modification of the potential surface for realizing the elementary processes and enables us more straightforward comparisons to the experiments in arbitrary compression and strain setups.…”